Radon-222 Exposure from Groundwater Ingestion and Tissue Lead as a Potential Indirect Biomarker of Internal Exposure in Wistar Rats
Olive-Adelodun Adetola Olufunke
Department of Physics, Hall Mark University, Ijebu-Itele, Ogun State, Nigeria.
Oni Emmanuel Abiodun
*
Department of Pure and Applied Physics, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria.
Aremu Abraham Adewale
Department of Pure and Applied Physics, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria.
Oladapo Olaonipekun Olukunle
Department of Science Laboratory Technology, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria.
Oyero Peter Olaoluwa
Department of Physics, Adeleke University, Ede, Nigeria.
Oni Olatunde Michael
Department of Pure and Applied Physics, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
Groundwater is the dominant source of drinking water in Southwest Nigeria, yet radon-222 (Rn-222), a naturally occurring radioactive gas linked to internal radiation exposure, remains largely unmonitored in this supply. This study investigated tissue lead (Pb) concentration as a potential indirect biomarker of internal Rn-222 exposure using a Wistar rat model. The rationale was based on the radioactive decay relationship between Rn-222 and its short-lived progeny, followed by the longer-lived Pb-210 in the U-238 decay series, together with the potential for retention and redistribution of Pb within biological tissues. Fifty groundwater and surface water samples from ten locations in Ogbomoso, Southwest Nigeria, were analysed for Rn-222 using a RAD7 electronic radon detector. All borehole samples exceeded the U.S. EPA reference level of 11.1 Bq/L, with concentrations ranging from 75.4 to 208.6 Bq/L. Borehole water (84.7 Bq/L) and surface water (3.5 Bq/L) were subsequently administered to exposed and control groups of rats, respectively, for 21 weeks. Tissue Pb concentrations were quantified by Atomic Absorption Spectrometry at 7, 14, and 21 weeks, alongside the estimation of absorbed radiation dose. Pb accumulation increased progressively with exposure duration in all tissues, with the kidney recording the highest concentration (0.320 ± 0.018 μg/g in exposed females at 21 weeks) and adipose tissue showing the highest radon activity concentration (17.87 Bq/kg). Linear regression revealed statistically significant positive correlations between absorbed dose and tissue Pb concentration in every tissue examined, with the strongest relationships in the stomach (R² = 0.819) and liver (R² = 0.817). Sex-related differences were minimal. These findings suggest that tissue Pb accumulation, particularly in the stomach and liver, may serve as a reliable biomarker of chronic internal Rn-222 exposure from groundwater ingestion, supporting the case for regulatory attention to radon in Nigerian drinking water sources.
Keywords: Radon-222, groundwater, lead biomarker, Wistar rats, absorbed dose, Southwest Nigeria